1. Field of the Invention
The present invention relates to a wiring board, and more specifically, to a wiring board on which electronic components, such as an IC, are to be mounted, and to a wiring board module.
2. Description of the Related Art
A high-frequency module in which various components, such as an IC component, a crystal oscillator, and other surface mount components, are mounted on the mounting surface of a ceramic wiring board is known (see, for example, Japanese Unexamined Patent Application Publication No. 2002-9225 (Patent Document 1)). Various mounting lands are provided on the mounting surface of this wiring board. Normally, one mounting land is provided for each external terminal of the mounted components. Generally, the sizes of these mounting lands are selected according to the sizes of external terminals of the mounted components. The reason is that mounting a large-size component requires a large amount of solder, and therefore, requires large-area lands.
FIG. 8 is a plan view showing an example of a conventional ceramic wiring board module 50. A crystal oscillator 1 and an IC component 2 are mounted on the mounting surface 51a of a wiring board 51, which are shown by an alternate long and short dash line, and other surface mount components (not shown) . Mounting lands 52 for the IC component2, mounting lands 53 for the crystal oscillator 1, and mounting lands 54 for other surface mount components are provided on the mounting surface 51a. The area of the mounting lands 53 is substantially larger than the other mounting lands 52 and 54.
However, when the large-area mounting lands 53 are provided, large local swells (protrusions) are generated at the locations of the mounting lands 53 on the mounting surface 51a of the wiring board 51. This is due to the difference in shrinkage factor between the wiring board body and the mounting lands upon firing. In general, when fired, a board body made of ceramic substantially shrinks, while mounting lands do not substantially shrink. Therefore, when large-area mounting lands are provided, the mounting surface of the wiring board swells.
FIG. 9 is a graph showing the amount of swell in the X direction in the conventional wiring board 51 measured throughout the wiring board 51 at predetermined pitch intervals. FIG. 10 is a graph showing the amount of swell in the Y direction in the conventional wiring board 51 measured throughout the wiring board 51 at predetermined pitch intervals. In FIGS. 9 and 10, the vertical axis indicates the amount of swell (μm), and the horizontal axis indicates the locations of measuring points.
In the circles P1 and P2 in FIG. 9, large local swells caused by the mounting lands 53 are regenerated. These swells prevent small-size electronic components from being mounted in a desired location place and/or prevent electronic components from being mounted horizontally.